My TOSHIBA SATELLITE A200 laptop badly needs some repair

Hi there...I wanna ask you for some opinion about my problems with my (otherwise satisfying) toshiba satellite A200 laptop.

1. my LCD ... I have some areas on the surface of the LCD, which are too bright, or some look like there is a dirt underneth the protective glass cover... they are almost invisible when looking straight at the display...but they are apparent when a homogenic e.g. white desktop is displayed....
And that's not all cause even the backlighting seems to be damaged somehow...I see darker areas near the display's borders...also in these areas the colors are significantly disturbed...

2.the bigger problem, however, concerns cooling...or...what supposed to act liek cooling, but does not do so any more....I won't lie to you.. the machine is 1 year old, and it was frequently exposed to humidity, heavy dust and ash-contaminated room for extended periods (running for days non-stop)...I soon noticed degradation in cooling performance, which finally resulted to overheating of CPu, GPU under heavy load...
SO.....I decided that this must be caused by heavy contamination of laptop inside area, especially I suspect heatsinks to be filled with dust...and...the logical course of action was to take the damn box apart and clean it up....maybe work out some upgrade for cooling system (e.g. use arctic silver paste..)...however...taking the damn thing aparat turned out to be not that simple as I had thought before (having exhaustive experiences with desktop hardware).....I unscrew every single screw I found, dismantled every cover I could find and removed all the devices I was able to....But after removing ALL the screws the damn thing still held together... Today I took a look at some guides...and maybe I just had to remove the optical drive and that could be it...I did not use any guide back then, though, and I ended up surrendering. THE BAD THING WAS, that when I tried to boot it when partially disassembled, It refused to to do...Hitting power button just did nothing or simply turned on the machine for a bried periof of seconds...then it just shut down...So, these nightmares came to me that I killled my laptop...and I decided to mount everything back as it was......result : THE PROBLEM seemed to be resolved at first, but it was not, as I soon realized. NOW...when I turn the PC on, it boots normally most of the time....but (especially under load) ... it spontaneuously turns off...AND...when I start it again...It keeps shutting down when starting to load windows (sometimes it shuts down even sooner)..... after a few tryies the thing boots up, but then you may bet that it will die very soon....I discovered some characteristics in this behaviour.. It tends to improve byt itself by some more boot attempts...and then eventually it last running for a few days straight....then..out of nothing...shuts down again and refuses to work for some next boot attempts.
IMPORTANT FINDING no. 2: it seems to be of greatest help to boot the system ON BATTERY POWER....thus it almost always boots up win.....AND....also I experience problems with MOUSE after such failure occurs and PC boots up again....What kind of problems ? I click something and it does nothing...or executes a different command like some other area has been clicked...this behaviour also tends to improve with succesfull booting and running over time....The symptoms are the worst when booting up for the firts time succesfully after such failure I wrote about above....

SO...please post your opinions about what may be the cause of these problems (well, the screen I suppose is mechanically damaged, not much science required here ... maybe just tell me how much doest it cost to replace LCD .. (I suppose it will be rather much).....HOWEVER, i am really curious about possible explanations and solutions to this... power issue (I believe it's definitely some kind of power issue, at first I thought it was overheating but then I revoked that.....overheating is a separate problem, and the one I know how to solve.....)...It even occured to me that it may be a HDD damage, which causes these shutdowns..but I don't think that is the case....

additional info: I ruled out OS problems (two dif wins installed a few times)...nad also any other software realted possible causes. I even tried disabling one core, and locking CPU on 1000MHz, helped a bit....but the shutdowns still occur... So I don't believe it's CPU overheating..nor GPU overheating (cause when GPU overheats it crashes the application first, not instantly shuts down...

Thank you for your opinions and suggestions